Miscellaneous. 87 
between the membrane of the test and the madreporic plate. Other 
tubular glands, situated on the opposite side of the cesophagus, in 
the thickness of the mesentery itself, open in part with this ex- 
cretory duct, and in part directly beneath the madreporic plate, 
the pores of which probably give issue to the secreted liquid. It is 
to be observed that, by the intermediation of the infundibuliform 
space situated below the madreporic plate, the circulatory apparatus 
and this glandular apparatus communicate with each other, so that 
an injection driven through the supposed heart may descend again 
through the sand-canal. 
In the Spatangidee (Amphidetus), which have been said to have 
no trace of a heart, I have found a gland exactly similar to that 
which hitherto has been regarded as the heart in the Echinida. 
Lastly, I have ascertained, by varied experiments, that the water 
which fills the cavity of the test of the sea-urchins can only pene- 
trate them slowly and by endosmose, either through the buccal 
membrane or through the ambulacral tubes. When sea-urchins 
have lived for some time in sea-water coloured with aniline, we 
very regularly find the entire cesophagus and the siphon by which 
it communicates with the point of reflexion of the intestine coloured 
red. There has consequently been an introduction of water into 
the intestine by this course, and a possible passage of a part of this 
water into the general cavity through the walls of the digestive tube. 
—Comptes Rendus, November 16, 1874, tome Ixxix. pp. 1128-1132. 
Embryology of the Ctenophora. By ALpxasNpER AGASSIZ. 
The question of the systematic position of the Ctenophora can 
now, thanks to the greater knowledge we have of their embryology, 
be treated more intelligently. The position taken by Vogt, who 
follows Quoy in removing them from the Acalephs altogether, and 
associating them with the Mollusks on account of the apparent 
bilaterality so strongly developed in some families (Cestum, Bolina, 
and Mertensia), seems not untenable. The nature of their relations 
to Echinoderms, Polyps, and Acalephs, as well as the general rela- 
tions of the Coelenterata to Echinoderms, may be discussed again, 
especially as having an important bearing not only on the value of 
the Coelenterata as a primary division of the animal kingdom, but 
also on the limits of the Radiata, and the possible affinities of the 
Sponges and Ceelenterata suggested by Hiickel*. A still more im- 
portant point developed from this embryology is its connexion with 
the Gastrea theory of Hackelt, for which he claims that it will 
supplant the type theory, and give us in its place a new system 
based upon the homology of the embryonic layers and of the primi- 
tive digestive cavity. Hickel attempts, in his G'astrea theory, to 
find an explanation for the natural development of species from a 
purely mechanical cause, and has been bold enough not only to 
* E. Hackel, ‘ Die Kallkischwamme,’ Berlin, 1872. 
+ E. Hackel, “ Die Gastrea-Theorie,” Jenaische Zeitschrift, ix. 1874. 
